In recent years, from the social requirement of lower fuel consumption and less exhaust emission, an electric automobile and a hybrid automobile, each of which is mounted with an AC motor as a power source of a vehicle, is drawing attention. For example, in some of the hybrid automobiles, a DC power source made of a secondary battery or the like and an AC motor are connected to each other via an electric power conversion device constructed of an inverter and the like, and the DC voltage of the DC power source is converted into AC voltage by the inverter to thereby drive the AC motor.
In the control device of the AC motor mounted in the hybrid automobile and the electric automobile, in general, a feedback control is performed on the basis of the phase current sensed value sensed by the current sensor. For example, in a sine wave PWM control mode, dq axis current calculated values obtained by dq transforming the phase current sensed value are fed back to current command values. Further, in a square wave control mode, a torque estimated value is estimated from the dq axis current calculated values and the torque estimated value is fed back to a torque command value.
On the other hand, there is provided a technique of using Fourier transformation for a control technique of an AC motor. For example, an object of a technique disclosed in a patent document 1 is to reduce a torque pulsation by Fourier transforming a torque sensed value directly sensed by a torque meter or a torque estimated value estimated on the basis of a current sensed value and by extracting arbitrary order component and by performing a learning control in such a way that the Fourier coefficient of the order becomes 0.
In the meantime, in the control device of an AC motor, there are cases where a phase current has higher order components superimposed thereon and where the phase current is offset.
When the phase current has the higher order components superimposed thereon, for example, the command duties of the respective phases obtained as the result of the current feedback control also have higher order components superimposed thereon, which hence results in making also noise components such as the switching noises of the inverter include higher order components. These noises are not desirable in the aspect of silence. In particular, in an overmodulation range, a PWM pulse includes higher order components and hence the phase current has the higher order components easily superimposed thereon, which presents a problem of causing larger noises.
Further, when the phase current is offset, an electric first order torque variation and power variation will be caused. In a control device of an AC motor mounted in a vehicle, the torque variation vibrates the vehicle and hence is not desirable. The power variation varies a power source current and a power source voltage and hence is not desirable in terms of the protection of parts.
In this regard, that the phase current is offset means a center value of a current amplitude is offset from a reference value of 0 [A] learned on the basis of the phase current when the device is started up. This is mainly caused from the temperature characteristic of a circuit for receiving an output signal of the current sensor and the amount of offset tends to gradually increase as the control device of the AC motor is continuously driven.
Further, in the square wave control mode of a three phase AC motor, the respective phases are on and off once every one period of an electric angle, that is, are switched on and off 6 times in total and hence the phase current has sixth order components synchronous with the switching superimposed thereon. When it is tried to remove the sixth order components by a low-pass filter, a current vector is likely to be excessively smoothed, which hence is likely to be detrimental to recognition. Therefore, a torque feedback has a gain forcibly made lower, which results in reducing a torque response.
For the problems described above, in the technique of the patent document 1, Fourier transformation is only applied to a torque sensed value or a torque estimated value and the object of the technique is manly to reduce a torque pulsation. Hence, by the technique of the patent document 1, it is not possible to reduce noises caused by the higher order components and to prevent a harmful effect produced by the offset of the phase current.
[Patent Document 1] JP-A-2010-57218